Coronavirus (COVID-19) vaccine certification: evidence paper

4. The use of baseline measures

A number of baseline measures are still in place in Scotland including:

• Wearing face coverings in public indoor settings including public transport
• Providing your contact details when you go to places like pubs, cafes and restaurants
• International travel – testing and quarantine requirements^[69]

In addition guidance is still in place recommending working from home if possible.

These baseline measures aim to reduce the likelihood of infected people mixing with others and infecting them. Wearing face coverings helps reduce the risk from a potentially infectious person in any given setting.

Detailed guidance is available for all sectors of the economy and society on how to operate with lower risk. In addition organisers of outdoor events of more than 5,000 and indoor events of more than 2,000 have to apply for permission and provide the local authority with a risk assessment.

Sage noted in April 2021 that:

"there are three main ways in which baseline measures can reduce transmission (from most to least effective)"^[70]:

1. Reducing the likelihood that people who are infectious mix with others.

The most effective baseline measures are likely to be ones which reduce infected people mixing, such as an effective test, trace and isolation system (high confidence)^[71].

2. For those potentially infectious people who are not isolated, reducing the likelihood that they enter higher risk settings or situations.

EMG SPI-M advises that the next most effective baseline measures aim to eliminate or substitute some of the higher risk situations where transmission could occur. This could be by using a certification scheme based on negative testing, vaccination, or proof of prior infection^[72]. Other important ways would be by minimising the frequency and duration of exposure such as encouraging outdoor interactions, working from home, and generally reducing the number, size, and duration of interactions^[73].

3. Decreasing the transmission risk from a potentially infectious person in any given environment^{[74] [75]}.

EMG SPI-M advises that to decrease the risk of transmission from an infectious person the following non pharmaceutical interventions (NPIs) should be considered:^[76]

• Physical distancing (to reduce risk from respiratory droplets and short-range aerosols)^{[77] [78] [79]}
• Ventilation (to reduce risk from long duration exposure and far-fields aerosol transmission)^{[80] [81] [82]}
• Face coverings (to reduce emission of virus and exposure to droplets and larger aerosols)^[83]. Other forms of barriers (e.g. Perspex screens) may provide some protection from droplets in some circumstances though consideration needs to be given to airflows, as in some cases they may increase risk of aerosol transmission.
• Hand hygiene and surface cleaning (to reduce risk from fomites)^[84].

These mitigating measures interact with each other and as such it is difficult to estimate the effectiveness of each baseline measure. However, for example, EMG SPI-M advises that theoretical effectiveness for a good quality face covering is likely to be around 50-90% for smaller aerosols and greater for large droplets^[85]. A number of large-scale studies and reviews from data in other countries suggest the impact on transmission of wearing a face masks is typically in 6-15% range, but potentially up to 45%^[86].

A complex set of factors interlink to determine the exact impact that various baseline measures have on reducing transmission; including level of compliance, quality of face covering or mechanical air ventilation systems and the physical environment etc. In addition, the effectiveness of each baseline measure or package of baseline measures will also vary depending on the demographic of people in attendance and their attitudes towards compliance.

SAGE suggest that:

"It is highly likely that transmission will increase in autumn and winter"^[87].

The reasons for this are due to people interacting with others inside rather than outside, and closing doors when the weather gets colder as well as seasonal social activities related to mid-term breaks and holidays. For this reason SAGE suggest that stronger measures may be beneficial in the autumn and winter^[88].

The vaccine certification scheme as proposed for Scotland is targeted towards higher risk settings or events and will be used in conjunction with the NPIs listed above^[89] to further enhance the overall preventative impact. As part of this package of mitigation measures, a vaccine certification scheme should ensure that only fully vaccinated individuals are present at these events reducing the risk of infection and severe illness leading to hospitalisation amongst the attendees.

SAGE considered with a medium confidence that a certification scheme could potentially have medium effectiveness^[90]. However they also warned that "certificates should also not be used to replace other measures to protect high-risk individuals"^[91].

Notably SAGE has suggested that "the prevalence of infection in the community will have an important impact on the level of risk and effectiveness of certification which may be very effective when prevalence is low, but less effective at high prevalence"^[92]